1. Field of the Invention
The invention relates to a product for fluidic applications with at least one surface segment provided to come into contact with the fluid flowing in a flow direction, wherein in the segment coming into contact with fluid are formed ribs of particular length and shape, of which adjacent ribs delimit between them in each case a valley. The invention also relates to a method for production and use of such a product.
2. Description of Related Art
Products of the type cited above are for example sheets or pipes or other flow bodies made therefrom, through or over which a flowable medium flows in practical use. Such products are used for example in the production of heat exchangers for solar thermal plants, as suction pipes for suction devices used in domestic or industrial apparatus, or other applications. With a view to an optimum energy use, in these and comparable fluidic applications one essential construction objective is to reduce flow losses to a minimum.
The fluid flowing over the products according to the invention can be a liquid such as water, oil, a suspension or dispension, a gas or gas mixture such as for example air, oxygen, nitrogen, argon or similar. The fluid can be mixtures of the same phases and also multiphase media such as gas-liquid or particle-fluid mixtures or particle-gas flows. Individual phase parts can have concentration differences. Also a substance exchange can occur within a phase or between the phases of the flowing fluid.
The processes used for the production of pipes, sheets and sheet films, and films in general, vary greatly. Sheets, sheet films and films made from steel or light metal materials are normally hot- or cold-rolled in the production process. Where they consist of corrosion-sensitive materials, they are normally also coated. Sheets made of non-corrosion resistant steels are normally coated with zinc, tin, zinc-magnesium. In addition or alternatively a paint layer can be applied.
In the production of pipes suitable for fluidic applications from sheet metal, the sheets are normally formed into a slot profile. The resulting slot is then closed by a welding process. Alternatively pipes can be made seamlessly from round castings.
A common feature of all known processes for production of components intended for fluidic application is that the surface structure of the products generated according to the current prior art have the following features:                The surface structure is stochastic in nature and described only imprecisely. To describe the surface topography and roughness, statistical mean values are used such as for example the arithmetic mean roughness Ra, the maximum roughness depth Ry, the mean roughness depth Rz etc.        In the production of sheets, the topology or roughness of a sheet can be influenced by texturing the working rolls used for hot or cold rolling of the sheet. Thus by corresponding roll texturing, the key values listed above can be influenced and thereby the visual impression of the surface, the paintability or deformation behaviour in subsequent moulding steps such as deep drawing and pressing. The surface structure which can be generated in this way however remains substantially stochastic in nature.        To describe the central properties here essential for the fluidic behaviour of product surfaces, normally specific key values are used such as sand roughness, coefficient of friction X, resistance count and similar empirically determined key values to describe the friction and the pressure loss occurring at the surface under the flow in each case. The key values concerned are influenced firstly by the nature of flow (laminar, turbulent) and secondly by the material and process used in production of the product coming into contact with the flowing fluid in each case. Thus for a steel pipe with longitudinal seam welding, new roller skin, the value for the equivalent sand roughness k lies typically in the range 0.04 to 0.1 mm (stochastic).        
With a view to the efficient use of resources and environmentally and climate-friendly use of energy—here electricity, pump power, fuels and similar—minimising flow losses in components through or around which fluid flows has particular importance. The energy required to deliver a fluid through a pipe or around a body depends on the friction losses which are generated in the fluid by the segment of the respective component exposed to fluid contact i.e. the inner surface of the pipe through which fluid flows or the respective wall of the body around which it flows. For a relative movement of component and fluid, at least the friction predominating between them must be overcome.
In the case of a fluid-carrying pipe, one factor is the pressure loss Dp which results when a fluid flows at speed v through the pipe. In the case of fluid flowing around the body, often the coefficient of friction cw is used as the comparative energy value.
Friction losses in components through or around which fluid flows arise in principle because in the contact zone, the relative speed between the fluid and the segment of the component it moistens is equal to zero. Between the fluid speed at the respective segment of the component and the flow further out, consequently in the case of a pipe flow, a speed profile forms ranging between zero at the pipe inner wall and a maximum speed in the centre of the pipe. In the case of fluid flowing around a body, a corresponding speed profile results which ranges from “zero speed” at the respective component to a maximum flow speed in the outer region lying spaced from the respective component and beyond influence.
In the region of contact between the flowing fluid and the component, characteristic flow regions are formed known as interface layers which decisively determine both the energy losses and the heat or substance transfer between the fluid and the wall/body. Depending on the observation site and the flow form (laminar or turbulent), laminar interface layers, transition regions and turbulence interface layers occur (both for the flow and for the temperature and substance concentration). Their spatial extent and the site of the change from laminar to turbulent can be determined as a function of the roughness k.
As stated initially, the roughness k is usually a stochastic value and is determined by the production process. When a sheet is produced by hot and cold rolling, the rolling parameters and surface roughness of the roll have a decisive influence on the roughness of the resulting sheet.
Another cause of friction losses or reduced heat transfer is deposits which result by particle or droplet transport from the flow region in contact with the moistened wall of the component. The deposit mechanism is determined firstly by chemical, metallurgical or thermodynamic regularities and secondly by the roughness of a surface.
Also the heat transport from a wall to the fluid flowing along it—either by cooling processes, heating processes or incident radiation—directly influences the fluid behaviour at the wall. Thus the heat exchange in particular influences the viscosity of the fluid concerned. As a result of the heat supplied or dissipated in the region of the contact surface, a viscosity gradient is formed between the regions close to the wall and the uninfluenced flow remote from the wall. In the case of a solar thermal or comparable application, the formation of this gradient has an influence on the entire heat transmission behaviour of the object concerned.
DE 36 09 541 A1 discloses that the flow resistance of a surface over which there is a turbulent fluid flow, such as for example an inner face of a pipe, can be reduced in that on the surface of the body concerned, ribs running in the flow direction of are formed which are separated from each other by sharp-edged ribs. The ribs are arranged in a plurality of staggered rib groups which each consist of a plurality of ribs arranged transverse or oblique to the flow direction next to each other and spaced apart. The ribs of rib groups successive in the flow direction of the fluid can be arranged offset to each other lateral to the flow direction. At the same time the ribs of the individual staggered rib groups have short extensions in the flow direction. Adjacent ribs arranged transverse to the flow direction delimit between them in each case a valley formed in the manner of fluting, the transition of which to the adjacent rib is rounded in a fluted manner. The staggered arrangement is regarded as decisive for the effect of said surface structuring. The targeted formation of short ribs arranged with the staggered offset can be particularly effective in minimising the flow resistance in the region close to the wall.
EP 1 925 779 A1 discloses in general that the flow resistance at surfaces over or around which fluid flows can be reduced, and in particular the efficiency of flow machines further increased, if the surface around or over which the fluid flows is given a surface structure creating a sharkskin effect. This is achieved by material removal, in particular by etching the surface, or by applying a coating forming the desired structure on the surface concerned.